Household appliances such as dishwashers and clothes washers typically have a plurality of cycles that require the introduction of clean water into the appliance. For instance, a clothes washer may have a soak cycle, a wash cycle, and a rinse cycle. Clean water is introduced into the appliance at the beginning of each of these cycles. However, before the clean water is introduced, any waste water present at the conclusion of the previous cycle in the operation of the appliance is discharged. The term "waste water" is used to designate water that has been used in one of the appliance cycles and is contaminated with soap, dirt, or the like. Waste water is typically discharged from the appliance into a sanitary system by a waste water discharge pump. The pump forces the waste water from the appliance, through a drain hose and into a stand pipe (or other drain) that communicates with the sanitary system.
A certain amount of back pressure is required for the most efficient operation of the waste water discharge pump, but only during operation of the pump. Back pressure that develops in the drain hose subsequent to the cyclic operation of the waste water discharge pump can result in reverse flow of the waste water through the waste water discharge pump and into the appliance. This occurrence is known as back-flow, and back-flow is undesirable not only because it contaminates the clean water introduced into the appliance during at least the subsequent cycle in the operation of the appliance but also because the existence of back-flow during operation of the pump can excessively increase the pressure head against which the waste water discharge pump must operate, which can damage the pump. To ensure against the undesirable effects of back-flow, a check valve, or back-flow preventer, is installed in the waste water discharge path, in order to assure a uni-directional flow of fluid therethrough.
One type of well known back-flow preventer commonly in use is typically referred to as a "duck call" check valve. A duck call check valve is manufactured by a two-step process. In the first step the substantially hollow, annular body of the valve--with a diagonally disposed divider wall extending across the hollow interior of the body portion - is molded. In the second step the liquid passageway is formed by slitting a portion of the annular body portion to which the downstream end of the diagonal divider wall joins the cylindrical interior surface of the body portion. In its final form, the valve comprises a generally annular body with an inner valve flap that extends diagonally across the interior of the otherwise hollow, annular interior of the body portion. The resulting configuration provides a normally closed check valve.
The exterior configuration of such a valve is reminiscent of a duck call. Hence, the name duck call check valve is commonly applied to such a valve. When fluid is forced through a duck call check valve, the fluid pressure acts against the valve member, forcing the valve member to fold laterally along a longitudinal reference plane and separate from the interior surface of the valve body along the location where the valve member had been slit during the manufacturing process, thereby creating a passageway through the valve. When fluid tries to flow back through the duck call check valve, the fluid pressure acts against the upstream surface on the valve member, thereby either closing the passageway or assuring that it remains closed inasmuch as the valve member tends to unfold to its closed position when the pressure of the exiting flow drops below a given value for the particular check valve.
One undesirable aspect of most prior art check valves employing resilient valve members, such as the duck call check valve, is the need to utilize a two-step manufacturing process. The second manufacturing step--which often requires an intermediate handling, or positioning, step (as exemplified by the need to slit the body portion when making a duck call check valve)--considerably increases the cost of the valve. The design of the valve is also undesirable in that the pressure required to open the passageway increases the amount of work that the waste water discharge pump must perform. That is, the effort required to maintain the valve in the open position imposes excessive back pressure on the waste water discharge pump.
Another undesirable aspect of the duck call check valve is the shape, and location, of the passageway once it is opened. The eccentricity of the passage through a duck call check valve unduly increases resistance to fluid flow and decreases the efficiency of the waste water removal system. When water is flowing through the duck call check valve, the opened passageway is disposed along one side of the cylindrical passage therethrough. As the water exits the valve, it collides with the corrugated interior surface of the drain hose and the velocity of the exiting fluid decreases, thereby increasing back pressure.
The duck call check valve, and most other back-flow preventer valves, are normally closed. A normally closed valve precludes heat dissipation from the pump outwardly through the drain hose when the pump is not operating.